The invention relates to a control method and control device for shifting an automatic, and in particular, non-powershift-capable transmission in a vehicle.
Vehicles with powershift-capable transmissions cannot generally use all gears since the long shifting breaks lead to a tractive power interruption, which are perceived as disturbing, particularly in the case of upshifting. The BMW i8 serves as an example. At its front axle, it has an electric engine that transmits power to the street via a two-gear transmission (not powershift-capable). Due to an RPM limit, the first gear can only be used up to approx. 120 km/h. Then, at the latest, a shift must be made into second gear to increase the vehicle's speed. In order to avoid this gear shift, up until this point, starting to drive in automatic mode with an optionally startable combustion engine (“Auto eDrive”) is already always performed in second gear. The first gear is only used in the pure electric mode (“Max. eDrive”) at a limited vehicle speed. Please refer to non-published DE 10 2014203668.2 by the Applicant for further technical background regarding this operation.
Starting to drive in the second gear, in the case of the BMW i8 in particular, has the following disadvantages.
On the one hand, you can only start driving with less wheel torque. In automatic mode (“Auto eDrive”), this causes a frequent start-up of the combustion engine. This results in a poorer electric driving experience.
On the other hand, in the case of full-load acceleration from a standing position, the electric engine can only render full performance in second gear at a higher speed than in first gear. You cannot start driving as quickly as in the first gear.
It is the object of the invention, in particular in the case of non-powershift-capable transmissions, to improve comfort on the one hand, and the ability to accelerate on the other.
The task is solved according to the invention by a control method and control device according to embodiments of the invention.
In the case of the control method according to the invention and in the case of the control device according to the invention, for shifting an automatic, in particular, a non-powershift-capable transmission, which has at least two gears, data of a driving-speed-related data source are received by at least one electronic control unit for a defined forecast range. Such data sources are, for example, navigation systems, car-to-car systems, transmitting road signs or other telecommunicated digital data. The data are such that the control unit can determine therefrom a region at least lying in the forecast range and having a limit speed below the maximum speed of the lower gear. If such a region was actually detected in the forecast range, either the lower gear is maintained or shifting is performed from the higher gear to the lower gear.
Shifting back to the lower gear is preferably performed only if a driver power request value (in particular, the accelerator pedal angle) lies below a defined (first) threshold and the driving speed lies below the maximum speed of the lower gear. The first threshold can be defined in such a way that the presence of a steady speed or a propulsion operation is ensured.
A shift is preferably made from a lower gear to a higher gear if, within a transition region between the region with the limit speed under the maximum speed of the lower gear and a region with a limit speed or a possible driving speed to be expected over the maximum speed of the lower gear, a driver power request value is under a defined (second) threshold and the driving speed is under the maximum speed of the lower gear.
The first threshold and the second threshold can be defined in the same way, or in terms of a hysteresis, be defined similarly, but differently.
The invention is based on the following considerations.
The disadvantages of a gear shift with comparably longer shifting disruptions only occur when the sample vehicle described above increases its speed to over 120 km/h—meaning over the maximum speed of the lower (e.g. first) gear. Therefore, the invention provides for a navigation-based shifting strategy. The vehicle recognizes if it is in a region with a limit speed under the maximum speed of the lower gear or if it approaches such a region (e.g. speed limit, 50, 60 or 80 km/h). In this region, a desire of the driver to accelerate beyond the maximum speed (e.g. 120 km/h) is unlikely.
So, for example, in an urban environment, according to the invention, the lower gear is maintained or shifted back into.
If the vehicle detects that it is approaching the city limits and will leave the city region (speed limit the same or over 100 km), the transmission shifts to the next highest (e.g. second) gear at a comfort-oriented moment, particularly at a steady speed and/or in a propulsion phase.
By means of this, particularly in the urban environment, driving with a higher electric wheel torque is possible, whereby, for example, the above-mentioned hybrid vehicle becomes more robust at start-up and a great electrical driving experience is achieved. In addition, the vehicle's absolute ability to accelerate in the urban environment increases.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.